The objectives of this research are to study the mechanisms and factors involved in the ability of the heart to regulate coronary blood flow and ventricular function from a physiological and mathematical point of view. This requires synergistic physiological and mathematical model development so that the physiological interferences are minimized and mathematical complications reduced. An isolated heart will be used. All pertinent mass transport and left ventricular variables will be recorded including perfusion pressure, coronary flow, arterial and venous PO2, tissue PO2, left ventricular pressure and corresponding time derivative. A mathematical mass transport model will be developed and constrained to duplicate the whole closed loop gains. Additional physiological measurements will be made and modeling assumptions relaxed to aid model verification and demonstrate the models adequacy (or inadequacy). These models should suggest critical physiological experiments that could provide definitive data concerning (a) the possible mechanisms of coronary blood flow regulation and (b) the mass transport factors involved in the modulation of myocardial O2 consumption and/or ventricular function. These models should clarify interpretation of PO2 histograms and might suggest clinically useful measures of tissue level phenomena. Further they could be used to predict the heart's response to stress and might suggest protective measures.